The long-range goal of the proposed research is to increase our understanding of the role of orienting and defensive responses in attention and information processing in humans. Over the past several decades extensive research on human subjects has failed to resolve many of the basic issues related to this question. The purpose of the proposed research is to conduct a systematic analysis of orienting and defensive responses in animal subjects from three different phyla, to analyze the changes in autonomic nervous system activity that accompany those responses, and to study the effects of those responses on attention and information processing i the three classes of animals. Achieving a fuller understanding of the function of orienting and defensive responses in a wide range of animal species may help us to understand the role of those responses in attention and information processing in humans. The first phase of the proposed research will systematically examine the cardiac and behavioral response to neutral, prey, and predator stimuli in selected amphibians (e.g., Bufo marinus), reptiles (e.g., Sceleporus poinsetti), and mammals (Sigmodon hispidus). Although the particular species chosen differ in a number of ways they are all subject to predation by the same predators and consume similar prey species. This will allow us to study the cardiac and behavioral responses of the different animal species to the same prey and predator stimuli, in the form of either real or simulated prey and predators. One major focus of the proposed research will be to record the changes in heart rate that occur during the various stages of predation and predator-escape. The first three stages of those sequences are the same and consist of (1) detection, (2) identification, and (3) assessment. In the predation sequence the assessment stage is followed by the capture response (e.g., approach and/ or attack). In the predator-escape sequence the assessment stage is followed by an escape response (e.g., flight, concealment, fighting). The cardiac changes that occur during these three common stages will be studied in both standard laboratory test chambers and simulated natural environments designed for each of the species to be studied. The second phase will employ specific pharmacological treatments to assess the underlying physiological mechanisms responsible for the various changes in heart rate that occur during the predication and predator-escape sequences. Subsequent research will attempt to relate those autonomic changes to attention and information processing. The third phase will focus on the role of the cardiac and behavioral responses occurring during the various stages of the predation and predator-avoidance sequences on attention and information processing. These results will be interpreted in terms of their significance for contemporary theories of attention and information processing in human subjects.